As a conventional device for absorbing pulsation of this type, the device shown in for example Japanese Patent Publication (A) No. 11-280904 is known. In the device shown in this publication, a fuel pump is equipped with a high pressure accumulator. This high pressure accumulator absorbs part of the pulsation of the pressure of the fuel discharged from the fuel pump to reduce the pulsation width of the fuel pressure and thereby stabilize the amount of injection of fuel.
The high pressure accumulator shown in this publication is provided with a thick disk shaped high pressure vessel constituting a case, a thin metal disk shaped diaphragm sealed and supported by the case at its peripheral edges and working with it to form a high pressure chamber, and a disk shaped plate for determining a limit of deformation of the diaphragm. The diaphragm is shaped as a flat sheet shape. Only one is used.
To assemble this high pressure accumulator, the case is welded with the outer edge of the diaphragm to seal them, then the plate is welded. After this assembly, a high pressure gas is charged inside from a gas charging inlet provided at the case. The gas charging inlet, for example, is structured for a double seal by a steel ball press-fit in the gas charging inlet and a stopper member welded to the low pressure side of the steel ball for sealing.
However, the high pressure accumulator described in this publication has a large number of parts and is complicated in structure as well. In production, the step of assembling and welding together the case, plate, and diaphragm and the step of charging the high pressure gas are different, so the number of steps and the number of welded parts are large and the production efficiency is poor.
On the other hand, Japanese Patent Publication (B) No. 7-45114 describes a method of sealing a sealed relay in which pressurized nitrogen gas is charged. The sealing system of this sealed relay is provided with a chamber for housing a workpiece, a workpiece support member for supporting the workpiece arranged in the chamber, and a laser emission unit arranged outside of the chamber and firing a laser beam to the workpiece in the chamber. The workpiece support member has a recess for holding a metal case of the workpiece, places a metal base on a flange provided at the opening of the metal case held in the recess, fills the chamber with pressurized sealing gas, then turns the workpiece support member so that the laser beam of the laser emission unit is fired against and welds the contacting parts of the flange and metal base over their entire circumference. By using such a laser welding method, it is possible to simultaneously charge a high pressure gas and perform welding. There is also no need for a hole for charging the gas.
However, in the method of sealing a sealed relay shown in this publication, since the metal base is placed on the flange of the metal case, the contact parts of the flange and metal base to be sealed are liable to deviate in position. If deviation occurs, the weld zone will become uneven in the circumferential direction. In some cases, the welding will be insufficient and will cause a poor seal. In particular, since the laser emission unit is positioned lower than the flange of the metal case forming the seal location and the laser beam is fired at an angle from below to the flange, at parts where the metal case sticks out from the metal base, the laser beam will not sufficiently reach the metal base resulting in easy occurrence of insufficient welding. As a result, there are the problems of easy leakage of the gas charged inside etc.